Variable frequency response



Oct. 27, 1953 A. D. RICHARDSON VARIABLE FREQUENCY RESPONSE GALv'ANoMETERFiled Dec. l0. 1948 INVENTOR. ARTHUR o. R/cHARoso/v N l q, N, .0 wunmwmuu )w w. u n mi f f g 1w ,r 7`K`j` if d Jwwwuw u w Patented Oct. 27, 1953UNITED STATES FATENT OFFICE VARIABLE FREQUENCY RESPONSE GALVANOMETERArthur D. Richardson, Pasadena, Calif., assignor ConsolidatedEngineering Corporation,

14 Claims. 1

This invention relates to galvanometers of the type adapted to respondto alternating or oscillating voltages.

In my copending application Serial No. 673,111, filed May 29, 1946, animproved galvanometer of the above type is described and illustrated. Inmy copending application, Serial No. 14,789, filed March 13, 1948, Idisclose a frequency controlling device adapted for use in galvanometersof this type. The present invention relates to improvements in such agalvanometer for damping the vibrating system to substantially eliminatethe natural period thereof. The damping means of the present inventionmay be used in the improved galvanometer as described in my copendingapplication or in substantially any galvanometer of this type with orwithout the aforementioned frequency controller. However, best resultsare obtained when the damping means is used in conjunction withfrequency control means.

A galvanometer, constructed as described in copending application SerialNo. 673,111, comprises an extremely light weight fine wire coil held insuspension by a pair o-f stretched wires anchored at opposite ends of asmall rectangular casing and comprising the axis of rotary motion of thegalvanometer coil. A pair of pole pieces are disposed in closeassociation with the coil and extend beyond the side of the case forengagement by a suitable magnet.

The damping means in accordance with the present invention comprises atubular memberdisposed around the coil and extending beyond the coil inboth directions. The upper end of the tubular member is open and thelower end is sealed around the lower suspension wire. The damping sleeveis lleol with a fluid of an appropriate viscosity-temperatureco-eflicient for the frequency of the particular instrument.

As above indicated the damping sleeve of the present invention isparticularly useful when ernployed in conjunction with the frequencycontrol means described in application Serial No. 14,789. This frequencycontroller comprises a curvilinear leaf spring adapted to fit snuglywithin the galvanometer case beneath the coil and slideable therein. Asolid disk is rotatably held in the spring and a cylindrical insert isrotatably mounted in the dish, the disl; and insert being slotted topermit passage of the suspension wire therethrough. By means of thisapparatus the effective free length of the lower end of the coilsuspension wire may be altered by rotating the insert with respect tothe disk so as to crimp the wire between the opposite ends of the insertslit and moving the spring-disk assembly lengthwise in the case. Thesuspension wire is centered by rotating the disk within the spring.

When using the damping sleeve of the invention in the absence of thefrequency controller, the lower end of the sleeve is sealed by a rigidplate through which the suspension wire passes. The frequency of theinstrument is thus established by the location of this plate. When thedamping sleeve is used in conjunction with the frequency controller thelower end thereof is sealed with a flexible membrane or cap which,although having an effect on the frequency, does not definitelydetermine the same as a function of the location of the membrane. Thefrequency controller is useful in the assembly of the instrument todetermine the correct location of the sealing membrane, and in theassembled instrument to fix the frequency thereof,

A feature of the invention is the construction of the damping sleevewhich comprises two telescoping tubes. In assembling the apparatus thelower tube is adjusted longitudinally to the correct position withrespect to the desired frequency and is thereafter affixed to the uppersleeve. When the diaphragm is sealed across the open end of the adjustedlower tube, it will be in the proper position to establish the desiredfrequency or to cooperate with the frequency controller to establish thedesired frequency.

The damping means of the invention together with the methods of usethereof will be more clearly understood from the following detaileddescription taken in relation to the accompanying drawings in which:

Fig. l is an elevation view of a galvanometer of the type described inmy aforesaid copending application;

Fig. 2 is a sectional elevation of the galvanometer of Fig. 1 showingthe position of the damping sleeve and the frequency controller; and

Fig. 3 is a lsectional elevation of the lower portion of thegalvanometer showing a modified form of damping means particularlyadapted to be employed in the absence of a frequency controller.

The galvanometer shown in elevation in Fig. 1 and sectional elevation inFig. 2 is substantially similar to the instrument described andillustrated in the aforementioned copending applications and comprises acasing l!) in the form of a square or rectangular prism the length ofwhich is many times greater than its cross sectional dimensions. Thecasing comprises an elongated back piece l i, two sides I2 and I3 and acover accuses l EA which may be removed to expose the inside of theinstrument.

A. pair of pole pieces it, l5 are mounted through the sides lil, I3respectively of the casing and denne a gap iii aligned on thelongitudinal axis of the oase. The pole pieces extend outwardly from thecase where they are connected to a magnet (not shown).

There is suspended in the gap IB between the pole pieces, an elongatedcoil il of une wire shaped to occupy a very small cross-sectional area.The coil il is composed of fine insulating wire, such as No. 48 enameledor even liner. The Winding is preferably done in such a manner that thecoil is substantially cylindrical in form with a circular cross section.Wires forming this coil are preferably cemented together so that thecoil maintains a rigid self-'supporting form,

For the purpose of suspending the coil in posin tion in the it there areprovided thin suspension wir iii, at each end of the coil. suspei ionwires are looped through the coil and the ends of the une wire formingthe coil I1 are brought out loosely and preferably are looped aroundrespective loops of the suspension wires ti, 252, thereby making thewires 2i, 22 effect, the terminals of the coil.

The wire iii has attached to it above the coil I'l a small rectangularmirror 2l. rlhe means of mounting the mirror 2l on the suspension wire2l is described in detail in application Serial No. 673,111. lor thepurpose of suspending this mirror and coil assembly centrally within thecasing, a wire holding member i, in the form of a cylindrical rod, ismounted at the upper end of the case and the wire 2l is affixed thereto.A compression spring .'i l held within an insulator portion. t3, ismounted in. the other end of the case and the wire 22 is hooked to thespring.

The wire holding member 3D is mounted through a bushing 33 and means areprovided for centering the suspension wire and coil on the longitudinalof the case. The entire mountn1 ing assembly is insulated from the caseby an insulating bushing 35i. The illustrated mounting means isdescribed in detail in my above meul tioned copending application SerialNo. 673,111.

The end of wire 22 is soldered to a hook (not shown) extending above thespring 3l. For the purpose of holding the spring assembly in a properposition within the end of the casing, there is provided a holdingmember 'i8 in the form of a horseshoe. This is wedged within the casingso that it bears against the sides thereof, and the tendency of thespring to expand pushes the inner end of the bushing 32 against thewedged end of the member t8 so that it maintains its position.

The length of wire 22 is such that when the aforementioned hook ishooked over the end loop of spring iii, the spring is compressedsomewhat against member 32 so that wires 2l, 22, are stretched withsubstantial tension. The hook (not shown) is of electrical conductingmaterial making contact with the spring 3| thereby putting the spring incircuit with the galvanolneter Coil. A suitable connecting wire 5t issoldered at the inner end of the spring 3l and is lead through thegalvanometer casing past the pole pieces lll, l5. The wire 5i] iscarried through the side IZ. of the casing through an insulating bushing5l into the interior of a terminal casing 52.

When the galvanometer is assembled, the mirn ror 2l is located adjacentan opening 54 in the wall i3 of the case. The reflecting surface of themirror is faced towards the opening so that light will shine on themirror and be reflected baci; through the opening. A suitable lens 553is held in juxtaposition to the opening. The lens may be held in a lensholder ill, the latter being rotatable about a pivot 58. The lens holdermay carry a second lens 5% which may be brought into alignment with theopening 54 if desired.

As described the galvanometer has a substantially hired frequencydeterminable by the length of the combined suspension wires 2l, 22 andthe coil il betwen the points of contact of the re'n spective suspensionwires with the mounting means at the upper and lower ends the case. rThefrequency controller E55, described in my co pending application SerialNo. 14,789, is adapted to be incorporated in the galvanometer as de"scribed and may be manually operated to adjust the frequency thereofover a comparatively wide range.

Briefly the frequency controller comprises leaf spring @t substantiallycircular in plan and having legs 58A, 69B projecting outwardly there--from to bear against thte walls of the galvanometer B. A disk 69 isrotatably held within the confines of the spring 68 and has a diametricslot 'it cut in a face thereof. The disk 69 is countersunlr at a pointin the slot to hold an insert l2 rotatably therein. The insert 'l2 isalso provided with diametric slot i3. rThe suspension wire is ledthrough the slot 'i3 in the insert lil and through the slot 'ifi in thedisk 59. The frequency controller is positioned in the case desiree andthe insert l2 is twisted so that the suspension wire is crimped betweenopposite edges or the slot lli. The disk is rotated to center thesuspension wire above the insert. The fren quency of the galvanometer isdetermined by tho location of the upper point of contact between thesuspension wire 2i. and the insert l2.

damping sleeve of the present inventioil comprises a tube @il rigidlymounted in the housing between the pole pieces around the coil Il andextending past the coil in both directions. A sleeve ill is mounted onthe lower end of the tube il!) and is closed at its lower end with aexible diaphragm or plate 82 through which the wire is sealed. A smallport 8d in the lower end of the sleeve Eil provides means for fillingthe tubes fit, Eil with a suitable fluid by means of a hypodermic needleor the like.

As mentioned above, the diaphragm 82 is sealed to the Wire 22, but beingflexible does not definitely nx the frequency of the instrument. However, the diaphragm does have an eifect on the frequency inasmuch as itimpedes vibration of the wire 22 at the point of contact. In assemblingthe damping sleeve in the apparatus, the

. sleeve 8| is free to slide on the tube 80. The

frequency controller 66 is adjusted to the approximately correctposition for establishing the desired frequency of the instrument beforethe lower end of the tube is sealed. This point is designated by a markon the case or the like. The frequency controller is moved and thesleeve Si is adjusted on the tube so that the lower end thereofcoincides with this predetermined point and is sealed to the tube inthis` position. The sleeve 8l may be affixed to the tube 80 by placing asuitable cementing compound around the upper edge of the sleeve, as at85. The flexible diaphragm 82 is then cemented on the end of the sleeveand sealed to the wire 22. Final determination of the frequency of theinstrument is obtained by adjusting the positioning of the frequencycontroller 6B below the diaphragm 82. Thereafter, the damping sleeve isfilled by injection through the port 84, with a fluid having a suitableviscosity temperature co-emcient.

The character of the iiuid injected in the damping sleeve is determinedas a function of the desired frequency of the instrument. Thus for afrequency of approximately 100 cycles per second it may be desirable touse a damping vfluid having a viscosity-temperature-co-efficient ofabout 135 centistokes. For an instrument having a frequency ofapproximately 3300 cycles per second a fluid having aviscosity-temperature co-efficient of approximately 1100 centistokes isappropriate. For frequencies intermediate this range the character ofthe damping fluid should should be altered accordingly. Theviscositytemperature-cefcient of the damping fluid to be used in anygalvanometer can be calculated with a fair degree of accuracy from thefollowing equation:

Xzygi (1) where The frequency and viscosity co-efficient rangeestablished by Equation 1 does not constitute a limitation of theinvention. The relationship indicated is that which I have found to besatisfactory, but not necessarily essential.

Referring to Fig. 3 a modification of the apparatus is shown which isadapted for use without the frequency controller. The galvanometcr shownin partial section in Fig. 3 is identical to that shown in Fig. 2, andlike parts are designated by like numerals. In this embodiment thetelescopic sleeve 3l of the `damping sleeve is employed to x thefrequency of the instrument. This is accomplished by sealing the lowerend of the sleeve 8| with a rigid diaphragm. or cap di) which bearsagainst the suspension wire 22. In this manner the contact of the wire22 with the rigid cap 99 determines the frequency of the instrument inthe same manner that contact of the wire 22 with the frequencycontroller 55 (Fig. 2) establishes the frequency.

In assembling the apparatus of Fig. 3 positioning of the sleeve 8l withrespect to the tube 80 is accomplished by trial and error until thecorrect frequency is established Awith the suspension wire 22 bound atthe lower end of the tube 8l. When the correct position has beenestablished the tube 8i is cemented to the tube 80 in the manner abovedescribed and the rigid diaphragm or cap 90 is cemented to the lower endof the tube and to the suspension `wire 22. Thereafter, the dampingsleeve is filled with appropriate fluid through the port 84.

Although the apparatus of Fig. 3 represents the simplest embodiment ofthe invention, the apparatus of Fig. 2, wherein the damping sleeve andfrequency controller are employed in conjunction with each other, has`the advantage of ease of adjustment and of assembly. Thus, as indicatedabove some diflioulty is encountered in fixing the exact position of thesleeve 8l in the apparatus of Fig. 3, having in mind that the rigiddiaphragm or cap 90 will and must determine the frequency of theinstrument. On the other hand the flexible diaphragm 82 on the lower end0f the sleeve 8| on the apparatus of Fig. 2 does not definitelydetermine the frequency of the instrument which may be simply determinedby adjustment of the controller 66. For this reason any error in thelocation of the diaphragm 82 can be compensated for by adjustment of thefrequency controller.

In either of the embodiments, the telescoping nature of the dampingsleeve has the advantage of permitting the use thereof withgalvanometers of any desired frequency. The sleeve may be adjusted inoverall length so as to permit operation at the desired frequency.Furthermore, the apparatus can be assembled and the frequencyestablished by actual test before the sleeve 8l is sealed to the tube80, and before the lower end of the sleeve Bl is sealed. Thereafter',and after the correct frequency has been established, the tube may befilled with a uid having characteristics suitable to the particularfrequency.

Although the invention has been described with relation to a particularsquare case galvanometer as described in my copending applications, itis apparent that it will find use in any galvanometers of this typeregardless of design.

claim:

1. A damping sleeve for a galvanometer having a coil suspended betweenthe poles of a magnet by upper and lower suspension means, the dampingsleeve comprising a first tube adapted to be stationarily mounted aroundthe coil between the poles of the magnet, a second tube fitting over thelower end of the rst tube and aiixed thereto, a flexible diaphragm`disposed across the bottom end of the second tube and sealed around thelower suspension means at a point above the lower end thereof, and afluid disposed in the tubes.

2. A damping sleeve for a galvanometer having a coil suspended betweenthe poles of a magnet by upper and lower suspension means, the dampingsleeve comprising a first tube adapted to be stationarily mounted aroundthe coil between the poles of the magnet, a second tube fitting over thelower end of the first tube and affixed thereto, a rigid diaphragmdisposed across the bottom end of the second tube and sealed around thelower suspension means at a point above the lower end thereof, and aiiuid disposed in the tubes.

3. A damping sleeve for a galvanometer having a coil suspended betweenthe poles of a magnet by means of upper and lower suspension means, thedamping sleeve comprising a first tube adapted to be stationarilymounted around the coil between the poles of the magnet, a second tubefitting over the lower end of the rst tube and affixed thereto, a rigiddiaphragm disposed across the lower end of the second tube and sealedaround the lower suspension at a point above the lowei` end thereof, thesecond tube being afiixed to the rst tube in such longitudinalrelationship that the rigid diaphragm establishes the frequency responseof the galvancmcter at approximately a pre-selected value, and a fluiddisposed in the tubes.

4. A damping sleeve for a galvanometer having a coil suspended in a casebetween upper and lower suspension means comprising a first tube adaptedto be stationarily mounted around the coil within the case, a secondtube fitting over the lower end of the rst tube and aflixed thereto,means sealing the end of the second tube at a Vpoint above the lower endof the lower suspension means, and having the lower suspension meanshaving a viscosity-temperature-co-efcient approximately equal to X wherelower end thereof, the tubes being lled with a l 10 damping uid, andmeans slidably mounted in the core below the diaphragm and engaging thelower suspension wire to cooperate with the diaphragm to x the frequencyresponse of the galvanometer.

ARTHUR D. RICHARDSON.

References Cited in the flle 0f this patent UNITED STATES PATENTS NumberName Date 1,616,754 Mechau Feb. 8, 1927 1,723,555 Legg Sept. 17, 19292,024,966 ChlOWSky Dec. 17, 1935 2,137,188 Whitman Nov. 15, 19382,425,407 Washburn Aug. 12, 1947 2.519 689 Morrow Aug. 22, 1950

